Normally, an optical disk, such as a DVD and a CD, has a light transmitting layer on a recording layer in which information is recorded. Information is recorded into or reproduced from the recording layer by irradiating light onto the recording layer via the light transmitting layer. In a case where the light transmitting layer has an error in thickness and has a difference from a specified value in this instance, spherical aberration occurs. There is known an optical disk recording/reproducing device configured to correct such spherical aberration, in which a collimator lens formed to be movable is mounted on the optical head, so that the collimator lens is moved to cancel out the spherical aberration according to the thickness of the light transmitting layer (For example, see Patent Document 1).
FIG. 14 is a perspective view showing the configuration of a collimator lens drive mechanism employed in a conventional optical disk recording/reproducing device. A lens drive mechanism 160 shown in FIG. 14 is configured to move a collimator lens so that spherical aberration is cancelled out according to the thickness of the light transmitting layer of an optical disk. It includes a reference shaft 161 and a sub-reference shaft 162 both disposed parallel to the optical axis and a collimator lens holder 163 supported on these reference shafts 161 and 162.
The reference shaft 161 and the sub-reference shaft 162 are immovably attached to a fixing portion of the optical head. The collimator lens holder 163 is supported on these reference shafts 161 and 162 to be movable by sliding in the optical axis direction. The collimator lens operated to move so as to cancel out the spherical aberration is mounted on the collimator lens holder 163. In other words, the lens drive mechanism 160 moves the collimator lens mounted on the collimator lens holder 163 back and forth and parallel to the optical axis direction by moving the collimator lens holder 163 back and forth along the reference shaft 161 and the sub-reference shaft 162.
The lens drive mechanism 160 includes, as drive mechanisms that move the collimator lens holder 163 back and forth along the reference shaft 161 and the sub-reference shaft 162, a DC motor 164 that serves as a drive source to move the collimator lens holder 163 and a gear mechanism 165 that converts rotations of the DC motor 164 into parallel movements along the optical axis direction and transmits the parallel movements to the collimator lens holder 163. Rotations of the DC motor 164 are converted into parallel movements along the optical axis direction by the gear mechanism 165 so as to move the collimator lens holder 163. The collimator lens is thus moved to cancel out the spherical aberration according to the thickness of the light transmitting layer of an optical disk.
The gear mechanism 165 includes a rack 166 attached to the collimator lens holder 163, a first gear 167 attached to the rotation shaft of the DC motor 164 for transmitting a rotational force of the DC motor 164, a second gear 168 to convert rotations of the DC motor 164 into parallel movements along the optical axis direction, a third gear 169 to transmit a drive force that has been converted into the parallel movements along the optical axis direction by the second gear 168 to the rack 166.
The rack 166 to which the drive force is transmitted from the third gear 169 is of a double structure in which two racks 166a and 166b are superimposed and the racks 166a and 166b are coupled with a spring 171 in order to eliminate a backlash between the rack 166 and the third gear 169.
When the collimator lens is moved using the lens drive mechanism 160, the DC motor 164 is rotated. The first gear 167 consequently starts to rotate. Rotations of the first gear 167 are transmitted to the second gear 168 and converted into parallel movements along the optical axis direction. The drive force converted into the parallel movements along the optical axis direction by the second gear 168 is transmitted to the rack 166 via the third gear 169.
The rack 166 is attached to the collimator lens holder 163 and the collimator lens holder 163 is supported on the reference shafts 161 and 162 to be movable by sliding in the optical axis direction. Accordingly, the collimator lens holder 163 is moved in the optical axis direction by the drive force transmitted to the rack 166 via the third gear 169. The collimator lens mounted on the collimator lens holder 163 is thus moved in the optical axis direction.
The lens drive mechanism 160 configured as above is able to move the collimator lens at a high degree of accuracy and is therefore able to cancel out the spherical aberration resulting from a variance in thickness of the light transmitting layer in a satisfactory manner.
Meanwhile, on the part of an optical disk recording/reproducing device, such as a DVD drive, incorporated into a notebook computer or the like, a reduction in thickness and weight of the notebook computer itself raises a need for the optical disk recording/reproducing device to become thinner and lighter.
The optical disk recording/reproducing device employing the lens drive mechanism 160 as described above, however, includes the DC motor 164 having a large diameter. Employing such a DC motor makes it difficult to achieve a thinner optical disk recording/reproducing device.
In addition, because torque of the motor drops off by merely making the diameter of the motor smaller, a larger amount of current has to be flown in order to generate torque as high as conventionally generated torque. In this case, a heat release value by the motor is increased due to a larger amount of current. However, because the optical disk recording/reproducing device that has been made thinner as described above does not have a sufficient space inside, heat cannot be released sufficiently, which poses problems that the torque drops off or the motor itself breaks.
Further, optical disks include a CD and a DVD as well as a BD (Blu-ray Disc) and an HD-DVD achieving the recording at higher density with the use of a blue laser beam, and a multi-DVD drive that records information in and/or reproduces information from these optical disks requires several types of objective lenses corresponding to the respective types of optical disks and optical systems corresponding to the respective types of objective lenses. The number of components therefore increases and it becomes more difficult to make the optical disk recording/reproducing device thinner and hence to release heat.
Patent Document 1: JP-A-11-259906